The Carrier to Noise ratio of the TS-940S may be improved by the following changes. This bulletin supersedes bulletin number 911 dated September 15, 1986.
Parts required:
PLL UNIT (X50-2020-00)
R120, 129 3.3 Kohm 1/6 watt carbon resistor RD14CB2C332J
R121, 124 680 ohm 1/6 watt carbon resistor RD14CB2C681J
C180, 181 .01 µF disc ceramic capacitor C91-0117-05
C184, 185 .33 µF 35V Tantalum capacitor CS15E1VR33M
RF UNIT (X44-1660-00)
R154, 155 3.9 Kohm 1/6 watt carbon resistor RD14CB2C392J
C193, 194 1 µF 25V Tantalum capacitor CS15E1E010M
Procedure:
On the PLL unit (X50-2020-00) remove capacitor C176, C180, and C181. Change resistor R120 and R129 from 470 ohms to 3.3 Kohm. Change resistor R121 and R124 from 1 Kohm to 680 ohms. Change capacitors C184 and C185 from .22 µF to .33 µF 35V tantalum capacitors. Install C180 and C181 in the positions shown in the accompanying diagrams. The use of new capacitors is recommended to improve reliability, don't try to reuse the old capacitors! Capacitors C181 and C180 should be attached to the foil side of the PLL unit.
On the RF unit (X44-1660-00) install the series RC circuit composed of R154 and C193, and R155 and C194, as shown in the accompanying diagrams. As the diagrams illustrate it is easiest to move C132 and C193 to the foil side of the board and install the series RC circuit on the component side.
This is an optional change and may not be performed under warranty. Time required for this modification is 1.5 hour or less.
PLL UNIT
RF UNIT
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